1. Field of the Invention
The present invention relates to a magnetic head support device for supporting a magnetic read/write head in a magnetic disk drive.
2. Description of the Prior Art
There are known magnetic disk drives having a magnetic head on a floating head slider for recording and reproducing information on the surface of a rotating magnetic disk. Such magnetic disk drives are in widespread use for information recording apparatus, In the magnetic disk drives, the magnetic head is supported on a magnetic head support device including a flexure. The magnetic head has a floating head slider mounted on the tip end of the flexure by a gimbal, so that the magnetic head can be lifted off the surface of the magnetic disk for quick movement to a desired track on the magnetic disk.
Recently, there has been a demand for high-density information recording on a magnetic disk with a magnetic head whose floating head slider is displaced off the magnetic disk by a small distance while at the same time maintaining reliable interfacing between the magnetic head and the magnetic disk. The floating head slider is kept out of contact with the magnetic disk under a negative pressure or a vacuum developed between the head slider and the magnetic disk. More specifically, when the magnetic disk is not rotating, the head slider is spaced a certain distance from the surface of the magnetic disk by an arcuately curved member on a leaf spring of the flexure of the magnetic head support device. When the magnetic disk is rotating at a constant speed and the head slider is moved toward the magnetic disk surface, a dynamic pressure starts being developed on the head slider. When the dynamic pressure and an external load acting on the leaf spring of the flexure are in equilibrium, the head slider is kept a slight distance off the magnetic disk surface under the vacuum developed in the gap between the head slider and the magnetic head. At this time, an air film is produced in the gap, and the rigidity of such an air film is about five times larger than the ridigity of an air film that is developed between a magnetic disk and a head slider lifted off the magnetic disk under a positive pressure. Consequently, the head slider stably follows surface undulations of the magnetic disk even when the gap between the head slider and the magnetic disk is small, When the speed of rotation of the magnetic disk is reduced, the dynamic pressure acting on the head slider is also reduced. When the dynamic pressure is reduced to the extent that the dynamic pressure and the external load are brought out of equilibrium, the head slider is displaced away from the magnetic disk surface back to the position it takes when the magnetic disk is at rest.
Today, magnetic disk drives are required to handle, i.e., read and write, an increasing amount of data and hence to process a large amount of data at high speed. Efforts to shorten the access time of magnetic heads are very important in the data processing technology related to the magnetic disk drives, and various technical developments have heretofore been made under such efforts. The access time is equal to the sum of a seek time that is required for the magnetic head to move radially to a circumferential line on the magnetic disk which includes a target track to be reached, and a wait time that is required for the target track to come to the magnetic head. Since the wait time is dependent on the speed of rotation of the magnetic disk, it cannot be shortened greatly. Actually, the wait time has remained almost unchanged for more than ten years in the past. Consequently, development efforts for shortening the access time of magnetic heads have concentrated on the reduction of the seek time in which the magnetic heads move radially to a circumferential line corresponding to a desired track on the magnetic disk. The seek time can be shortened by using an actuator of higher output power for moving the magnetic head support device and by reducing the weight of an angularly driven mechanism, including the magnetic head support device and the magnetic head, which mechanism is coupled to the actuator and is to be angularly moved radially over the magnetic disk. There is a limitation on attempts to increase the output power of the actuator because the capacity of the magnet of the actuator and the drive current supplied to the actuator cannot be increased substantially in view of the intensity of heat generated by the actuator, the weight of the actuator, and the cost of the actuator. As a consequence, it is necessary to design the angularly driven mechanism coupled to the actuator for a reduced weight and a required high rigidity in order to allow the magnetic head to access desired tracks at high speed.
The high rigidity and low weight of the angularly driven mechanism is also important from the stand-point of desired positioning control of the magnetic head. The magnetic head is positionally controlled by a closed control loop whose frequency range is limited by the resonance of the angularly driven mechanism in its vibration mode and is selected to be lower than the mechanical resonant frequency of the angularly driven mechanism so as not to adversely affect the closed control loop. Therefore, the higher the mechanical resonant frequency of the angularly driven mechanism, the stabler the magnetic head positioning control and the wider the frequency range of the closed control loop, with resultant high-accuracy positioning of the magnetic head.
With the conventional magnetic head support devices, as described above, the distal end of the flexure is shaped in a surrounding relationship to the head slider, and hence is relatively heavy. In order to allow the magnetic head to quickly access a desired track position on the magnetic disk, it is preferable hat the components coupled to the actuator be as light in weight as possible. Since the moment of inertia of an element is proportional to the mass of the element and the square of its distance from the center of rotation of the element, even a slight increase in the mass of the angularly driven mechanism that is positioned on the distal end of the magnetic head support device gives rise to a large increase in the moment of inertia, resulting in an obstacle to high-speed accessing movement of the magnetic head.
Inasmuch as the flexure is relatively heavy due to the configuration of its distal end that surrounds the head slider, the mechanical resonant frequency of the angularly driven mechanism or the magnetic head support device cannot be increased.
Another problem of the conventional magnetic head support device is as follows: Electric wires connected to the magnetic head extend across and around the edge of the distal end of the flexure in contact therewith so that they will not exert undue stresses on the magnetic head. However, the electric wires tend to be abraded by the flexure edge on account of vibrations caused by the magnetic head while the magnetic disk is rotating. As a result, the coverings of the electric wires may be peeled or torn off, causing a short circuit between the electric wires and the flexure, so that the output signal from the magnetic head will be cut off. Peeled- or torn-off fragments or dust particles of the coverings may be conducive to a crash of the magnetic head during operation of the magnetic head drive.